Many gonadal-steroid dependent neuroendocrine events and behaviors are thought to be mediated by steroid hormones acting through preoptic, hypothalamic and limbic system neurons which contain steroid-specific receptor proteins. The experiments in this proposal are designed to reveal, on a cell-by-cell basis the extrahypothalamic axonal connections of gonadal steroid hormone-concentrating neurons by using steroid autoradiography combined with retrograde neuroanatomical tracing. These experiments will reveal exactly how steroid-concentrating neurons fit in neuroendocrinologically or behaviorally relevant neural circuits. These experiments will examine the axonal projections of estradiol-concentrating neurons to the medulla and spinal cord. These experiments will also examine the axonal projections of androgen- and of progesterone-concentrating neurons to the mesencephalon, or medulla or spinal cord. The long term goal of all these experiments is to reveal, on a neuron-by-neuron basis, the neuroanatomical circuitry of gonadal steroid hormone- concentrating neurons in order to uncover mechanisms by which steroid hormones exert their powerful effects on the brain.